1. Field of the Invention
The present invention relates to call admission control techniques in an ATM (asynchronous transfer mode) switch, and more particularly to call admission control method and system for use in the ATM switch handling QoS (quality of service)—specified and QoS-unspecified virtual connections.
2. Description of the Related Art
In a local-area network (LAN) environment including ATM LANs and legacy LANs, a bandwidth management technique of ATM connections is needed to operate an application requiring a high quality, such as the case of video service.
As an example, a CAC ATM-connection bandwidth management system has been disclosed in Japanese Patent Application Unexamined Publication No. 10-271116. This conventional system is provided with a per-connection bandwidth monitor, allowing CAC (Call Admission Control) information to be calculated and displayed on screen. Further, the conventional system is provided with a simulator for predicting an available connection bandwidth.
Call Admission Control (CAC) is a function of determining whether a connection request is admitted or denied. More specifically, CAC determines whether the connection request can be accepted at SVC (switched virtual connection) call origination time. The connection request can be accepted only if the QoS for all existing virtual connections would still be satisfied if the request was accepted.
However, the conventional CAC has disadvantages in the case where a network using UBR (unspecified bit rate) traffic as normal traffic such as LAN emulation is connected to another network handling QoS-specified virtual connections such as CBR (constant bit rate) or VBR (variable bit rate) virtual connections.
More specifically, as shown in FIG. 4B, it is assumed that the full bandwidth of a line is B, of which a certain portion AQoS is already assigned to CBR/VBR traffic virtual connections and further a portion is assigned to a UBR traffic virtual connection. In this case, if the requested bandwidth R of a CBR traffic virtual connection is smaller than the available bandwidth AF=(B−AQoS), then the connection request is accepted regardless of the UBR traffic virtual connection, which may cause the UBR-traffic virtual connection to be suddenly disconnected.